The present invention relates to an ink jet recording method and apparatus for changing a mixture proportion of a plurality of types of ink based on an image signal to produce a fluid having a predetermined density and/or a predetermined color, and jetting this fluid to an image receiving medium to form an image.
U.S. Pat. No. 4,109,282 (which will hereinafter be referred to as a prior art reference 1) discloses a printer having a structure such that a valve called a flap valve is disposed in a flow channel for leading two types of liquid, i.e., clear ink and black ink onto a substrate for forming an image. The flow channel for each ink is opened/closed by displacing this valve so that the two types of liquid are mixed in a desired density to be transferred onto the substrate. This enables printout of an image having the gray scale information which is the same as that of the image information displayed on a TV screen. In this reference, it is disclosed that a voltage is applied between the flap valve and an electrode disposed on a surface opposite to the flap valve and the valve itself is mechanically deformed by the electrostatic attracting force to cause displacement of the valve. Furthermore, the ink is absorbed in paper by a capillary phenomenon between fibers of the print paper.
U.S. Pat. No. 4,614,953 (which will hereinafter be referred to as a prior art reference 2) discloses a printer head apparatus by which only a desired amount of multiple types of ink having different colors and solvent is led to a third chamber to be mixed therein. In this reference, it is disclosed that a chamber and a diaphragm-type piezoelectric effect device attached to this chamber are used as means for check-weighing a desired amount of ink and a pressure pulse obtained by driving this piezoelectric device is utilized.
Unexamined Japanese Patent Publication (KOKAI) No. 201024/1993 (which will hereinafter be referred to as a prior art reference 3) discloses an ink jet print head including: a liquid chamber in which a carrier liquid is filled; ink jet driving means disposed in the liquid chamber; a nozzle communicating with the liquid chamber; and a mixing portion for mixing ink to the carrier liquid in this nozzle. In this reference, it is also disclosed that adjusting means for adjusting an amount of mixture of ink to a desired value is provided.
Similarly, Unexamined Japanese Patent Publication (KOKAI) No. 125259/1995 (which will hereinafter be referred to as a prior art reference 4) discloses an ink jet recording head including: first and second supplying means for supplying types of ink having first and second densities, respectively; and controlling means for controlling an amount of supply of the second ink by the second supplying means so that a desired ink density can be obtained.
In this reference 4, employment of a micro-pump which has an exclusive heating device and is driven by its heat energy is disclosed as the controlling means. As this micro-pump, there is disclosed an example such that the heat energy is generated by the heating device and a pressure obtained by nucleate boiling caused due to the heat energy is used to drive, for example, a piston-type valve or a cantilever-like valve. Furthermore, this reference 4 describes that an inflow of ink can be effectively controlled in an area where the inflow is particularly small by adopting an actuator consisting of shape memory alloy to this valve.
Unexamined Japanese Patent Publication (KOKAI) No. 207664/1991 (which will hereinafter be referred to as a prior art reference 5) discloses a structure which is similar to that in the prior art reference 2 but which does not use a third chamber for mixing a plurality of types of ink.
Unexamined Japanese Patent Publication (KOKAI) No. 156131/1997 (which will hereinafter be referred to as a prior art reference 6) discloses an ink jet printer comprising a plurality of printer heads for forming an image having multiple colors based on image data. Ink and diluent are mixed at a predetermined mixture proportion to obtain diluted ink which is jetted from a nozzle so that a recording image is formed on a recording medium. The ink jet printer ejects the diluent from at least one printer head out of the multiple printer heads when all-white image data, that is, data representing that amount of mixture of ink is too small to realize a clear printing density, is input. As a result, a rapid change in tone (a tone jump) is prevented and the additional consumption of the diluent is suppressed to improve drying characteristics.
Unexamined Japanese Patent Publication (KOKAI) No. 264372/1998 (which will hereinafter be referred to as a prior art reference 7) discloses employment of a plurality of line heads in which ink ejection nozzles are linearly aligned. In this example, when the respective line heads are biased and arranged in a direction for feeding print paper and positions of nozzles in the respective line heads are biased relatively to a width direction of the print paper, pixel density can be enhanced. Furthermore, ink having a single color is ejected from each nozzle, and ink droplets having different colors are combined by ejecting ink having different colors in accordance with the line heads, thereby representing predetermined colors on the print paper.
In the respective prior arts disclosed in the prior art references 1 to 6, the different types of ink are mixed in advance to be then ejected, and an amount of supply of at least one type of ink among the multiple types of ink to be mixed is controlled. Therefore, a quantity of flow of ink having a desired density or color after mixing, i.e., a volumetric flow rate per unit time varies in accordance with a change in density or color. It has been revealed that, when the volumetric flow rate (which is also referred to as a flow rate hereinafter) per unit time of the ink fluid after mixing fluctuates in accordance with a change in ratio of mixture due to density or color in this manner, the quality of a finally-formed image is prominently deteriorated.
That is, in the image forming technique adopting the conventional ink jet mode described above, a volume of droplets formed by one ejecting operation (the ejection volume) is substantially constant, whereas a liquid flow rate of the mixed ink which is newly successively supplied to an ejection port (a jet generating portion) fluctuates. For example, when a supplied flow rate of the mixed ink is large, the supplied amount of the ink exceeds a quantity of droplets which can be ejected by one ejection operation, and the liquid remaining in the ejection port is mixed in the droplets for the next pixel. Further, when a supplied flow rate of the mixed ink is small, a part of the droplets for the next pixel is disadvantageously incorporated. This adversely affects the image quality.
In the prior art disclosed in the prior art reference 7, since one nozzle ejects single-color ink, one pixel is formed by multiple (three or four or more colors) ink droplets. Therefore, it is difficult to enhance pixel density, and another problem is that improvement of the image quality is restricted.
Moreover, any one of the aforementioned conventional ink jet systems includes one ink droplet ejecting means and a driving circuit of the means, i.e., a driver circuit (hereinafter referred to as ejection driver) with respect to one ink ejection port. That is to say, each ink ejection port is separately provided with a heater and a diaphragm for imparting an ink droplet ejection energy to the port, and these components are separately driven by individual driver circuits.
As a result, the ink droplet ejecting means is set to be inoperative with respect to the ink ejection port which does not contribute to image formation even during the image formation, and it is therefore possible to selectively eject only the ink droplets necessary for the image formation. However, for this purpose, it is necessary to dispose the same number of driver circuits as the number of ink ejection ports, and this complicates an apparatus structure.
The present invention has been accomplished under the circumstances as described above, and a first object thereof is to provide an ink jet recording method of mixing a plurality of ink liquids having different densities and/or colors to prepare the ink liquid having a desired density and/or color and jetting the ink liquid to an image receiving medium to form an image, so that image quality can be enhanced, an apparatus structure is simplified, and productivity can be enhanced. Moreover, a second object of the present invention is to provide an apparatus which is directly used for implementing this method.
According to the present invention, the first object is attained by an ink jet recording method for jetting an ink droplet of an ink liquid to an image receiving medium to form an image, comprising the steps of:
a) mixing a plurality of types of ink to produce the ink liquid before a plurality of ink ejection ports, a mixture proportion of the plurality of types of ink being changed based on an image signal, at least one of said plurality of types of ink being an image non-forming ink for substantially forming no image after drying out; and
b) ejecting the ink liquid from the respective ink ejection ports to form the ink droplets having the same volume, and to jet the ink droplets to the image receiving medium to form the image;
wherein ink droplet ejecting means is disposed in the respective ink ejection ports, and wherein at least two of said ink droplet ejecting means are simultaneously driven by a common ejection driver.
In the present invention, since at least one of the plurality of types of ink is the image non-forming ink, the amount of ink droplets ejected or jetted from the ink ejection port can always be managed to be constant. For example, the ink droplets which forms no image may be formed of the image non-forming ink, and the amount of ink droplets can always be managed to be constant. Therefore, the image can be formed while the plurality of ink ejection ports simultaneously eject the ink droplets.
The plurality of ink ejection ports may be divided into groups so that the ink ejection ports included in the same group are not adjacent with each other, and the plurality of ink ejecting means included in the respective groups may be simultaneously driven by the ejection drivers separately disposed for the respective groups. This is suitable for preventing interference among the types of ink which flow through the adjacent ink ejection ports. That is to say, when the ink flows into the adjacent ink ejection ports from a common ink channel, a timing for flowing into the adjacent ink ejection ports from the common ink channel deviates. In this case, two ejection drivers for driving the adjacent ink droplet ejecting means are further preferably set such that driving timing differs.
The first object of the present invention is also attained by an ink jet recording method for jetting an ink droplet of an ink liquid to an image receiving medium to form an image, comprising the steps of:
a) mixing a plurality of types of ink to produce the ink liquid before a plurality of ink ejection ports, a mixture proportion of the plurality of types of ink being changed based on an image signal, at least one of said plurality of types of ink being an image non-forming ink for substantially forming no image after drying out; and
b) ejecting the ink liquid from the respective ink ejection ports to form the ink droplets having the same volume, and to jet the ink droplets to the image receiving medium to form the image;
wherein one common ink droplet ejecting means is disposed for at least two or more adjacent ink ejection ports among said plurality of ink ejection ports; and
wherein said common ink droplet ejecting means is driven so that a constant amount of the ink droplets are simultaneously ejected from each of said adjacent ink ejection ports and are jetted to the image receiving medium to form the image.
In this case, since the common ink droplet ejecting means is used for the adjacent ink ejection ports to eject the ink droplets, a structure of an ink jet head (recording head) itself is simplified.
A flow rate of the plurality of types of ink (ink flow rate) can be controlled by various methods. For example, an ink supply pressure to each ink channel is kept to be constant, while a sectional area of each ink channel can be changed by a piezoelectric device. In this case, a diaphragm valve facing to the ink channel is opened/closed by the piezoelectric device. The piezoelectric device can be driven by a mechanically natural frequency (resonance frequency) of the device itself, and the time period for driving the device is changed by varying a pulse number of the frequency to control the flow rate. The piezoelectric device can also continuously control its distortion amount (an opening of the diaphragm valve) by an analog signal. In this case, the flow rate is controlled by a voltage of the analog signal.
When controlling all the flow rates of the plurality of types of ink by using the piezoelectric devices, a sum of cross sectional areas of the ink channels controlled by these piezoelectric devices is always set to be constant, and the amount of ink droplets ejected from the ink ejection port can be controlled to be substantially constant. For example, the sum of the pulse number for the time period for driving each piezoelectric device is controlled to be constant, or the total voltage of the analog signals is adjusted to be constant.
The flow rate supplied to each ink channel may be controlled by changing a discharged quantity of an ink feed pump. For example, the ink feed pump is driven by a pulse motor (stepping motor), and the ink flow rate can be controlled by a driving pulse number of the pulse motor. A usable ink feed pump is provided with at least one check valve disposed in the ink channel, a cavity disposed in the vicinity of the check valve, and a movable member for changing a capacity of the cavity. With such construction, the pump can discharge the ink by changing the volumetric capacity of the cavity.
The check valve used in the feed pump may be constituted in a geometrical shape in which a resistance in an ink flow direction is small and a resistance in a reverse direction is large. Such check valve having no movable portion can be produced by utilizing a method of manufacturing an integrated circuit or a printed wiring board or a method of manufacturing a micro-machine. The ink feed pump may be driven by a pulse motor.
When the ink feed pump driven by the pulse motor is provided to each of the plurality of ink channels, the total flow rate of the ink liquid can be controlled to be constant by always maintaining a total driving pulse number of the pulse motor for driving each ink feed pump constant, thereby the amount of ink droplets can be set to be substantially constant. The ink feed pump for use herein is preferably of a volumetric capacity type in which the discharge amount is proportional to a motor rotation amount. For example, a pump of a type such that a flexible tube closely attached to a circular case inner surface is squeezed in a defined direction from an inner periphery side by an eccentric ring, a vane pump, a gear pump, and the like are suitable.
The ink feed pump provided to each ink channel may be formed of the piezoelectric device and check valve. In this case, the piezoelectric device is a diaphragm valve driven by the mechanical resonance frequency inherent to the device. Each piezoelectric device is controlled in such a manner that the sum of pulse numbers (pulse numbers within a given time or a unit time) of the driving frequency of each piezoelectric device always becomes constant. This sets the total ejection volumetric flow rate of ink to be constant, and the amount of ink droplets can be set to be substantially constant.
Instead of the plurality of types of ink, a microcapsule dispersion liquid can be used in which some reactive materials out of a plurality of materials developing colors by reaction are microcapsulated and microcapsules are dispersed in the other reactive materials. In case that material permeability changes in accordance with a heating amount of a microcapsule wall, the heating amount of the dispersion liquid can be changed based on an image signal to change density and/or color based on the image signal.
After the dispersion liquid is allowed to develop the density and/or color based on the image signal, subsequent density change reaction and/or color development reaction (hereinafter referred to simply as color development reaction) is preferably restricted. For this purpose, for example, the dispersion liquid is irradiated with ultraviolet rays or other electromagnetic waves to decompose at least one type of reactive material, so that the reactive material may be changed to a light-color decomposed material having no coupling ability. In this case, the density or the color can be prevented from changing, even if the microcapsules are ruptured by impact, heat, and the like applied after image recording.
The second object of the present invention is attained by an ink jet recording apparatus for jetting an ink droplet of an ink liquid to an image receiving medium to form an image, said ink liquid comprising an image non-forming ink and an image forming ink, said apparatus comprising:
a plurality of ink ejection ports for ejecting said ink droplet to the image receiving medium;
first ink supply means for supplying the image non-forming ink to the respective ink ejection ports;
second ink supply means for supplying the image forming ink to the respective ink ejection ports;
a controller for controlling said first and second ink supply means in such a manner that a total amount of the image non-forming and image forming inks supplied to the respective ink ejection ports becomes constant and a mixture proportion of the image non-forming and image forming inks are changed based on an image signal;
ink droplet ejecting means separately disposed for the respective ink ejection ports; and
a common ejection driver for simultaneously driving the plurality of ink droplet ejecting means to simultaneously eject the ink liquids from the respective ink ejection ports to form the ink droplets having the same volume so that the ink droplets are jetted to the image receiving medium.
The plurality of ink ejection ports can be arranged in a direction completely or substantially crossing at right angles to a relative moving direction of the ink ejection ports and image receiving medium.
A plurality of adjacent ink ejection ports may be regarded as one group, and the ink droplet ejecting means for simultaneously ejecting the ink droplets from the ink ejection ports included in each group may be disposed for each group. In this case, not only the number of ejection drivers but also the number of ink droplet ejecting means can be reduced, and the structure of the ink jet head (recording head) is also simplified.
The ink droplet ejecting means can be formed by a heater for subjecting the ink liquid to nucleate boiling to eject the ink, a piezoelectric device, or a diaphragm driven by an electrostatic attraction force or an electrostatic repulsive force.
Instead of the plurality of types of ink, the microcapsule dispersion liquid can be used in which some reactive materials out of a plurality of materials developing colors by reaction are microcapsulated and microcapsules are dispersed in the other reactive materials.
In this case, when the material permeability of the wall of the microcapsule is changed by the heat of the heater, the density and/or color can be changed based on the image signal. Moreover, the liquid can be jetted to the image receiving medium by the ink droplet ejecting means formed of the diaphragm. Additionally, after the color development or density change by the heater, at least one type of reactive material may be decomposed to prevent unnecessary color development. For this purpose, an electromagnetic wave source (ultraviolet lamp or the like) may be disposed.